Substrate processing system, gas supply unit, method of substrate processing, computer program, and storage medium

ABSTRACT

The present invention is to provide a technique for uniformly processing a substrate surface in the process of processing a substrate by supplying a gas. The inside of a shower head having gas-jetting pores for supplying a gas to a substrate is partitioned into a center section from which a gas is supplied to the center portion of a substrate, and a peripheral section from which a gas is supplied to the peripheral portion of the substrate, and the same process gas is supplied to the substrate from these two sections at flow rates separately regulated. The distance from the center of the center section of the gas supply unit to the outermost gas-jetting pores in the center section is set 53% or more of the radius of the substrate. Moreover, an additional gas is further supplied to the peripheral portion of the substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application for patent enjoys the benefit of the right toJapanese Patent Application No. 2006-221675 filed on Aug. 15, 2006 andU.S. Patent Provisional Application No. 60/875,538 filed on Dec. 19,2006. The whole description in the aforesaid applications isincorporated herein by.reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a technique for processing a substrate,such as a semiconductor wafer, by supplying gases to it, and to a unitfor supplying the gases.

2. Background Art

In semiconductor device production processes, processing of a substratesuch as a semiconductor wafer (hereinafter referred to as a wafer),e.g., etching or CVD, is conducted by placing a substrate in aprocessing vessel, and injecting, onto the substrate, process gases froma gas supply unit called a gas shower head, set in parallel with thesubstrate.

On the other hand, the recent trend toward small-sized, higher-densitypatterns has brought to some processes such a problem that patternsformed on substrate surfaces by the processes are apt to be non-uniformin size. For example, in a process of making a line-shaped gateelectrode for a transistor by etching a gate electrode material layercovered with a resist mask, it is not easy to ensure a high selectiveetching ratio, and the resist mask disappears before the etching of thegate electrode material layer has been completed. For this reason, atechnique for etching a gate electrode material layer by the use ofsilicon nitride film (SiN film) as a hard mask is now examined.

However, lines made in SiN film by etching have such a strong tendencythat a curve of the within-film distribution of the line widths isconvex. In other words, the line widths tend to be greater in the centerof the film than at the edge. Since a depositing material is easilydeposited on SiN film, the non-uniformity of depositing gas distributionon a substrate surface readily affects the amount of a material to bedeposited on the sides of the lines. On the other hand, since it is moredifficult to exhaust a gas from the center of a wafer than from theedge, and the gas pressure is slightly higher in the center of a waferthan at the edge, the amount of the deposit is greater in the center ofa wafer than at the edge, and this difference in the amount of thedeposit is considered to affect the within-wafer distribution of linewidths greatly.

For example, in the process of etching SiN film 103 lying under aphotoresist mask 101 and SiO₂ film 102, as shown in FIG. 11(a), by theuse of a plasma of a process gas containing, for example, CH₂F₂ gasserving as a depositing gas and oxygen gas serving as an etching gas, asshown in FIG. 11(b), permissible variations in line size D are in therange of 10 nm or less. Lines not only in a high-line-density area of awafer 100, e.g., an area in which the ratio of metal lines to insulatinglayers between them is about 1:1, but also in a low-line-density area ofa wafer 100 that has so far been allowed to have relatively largevariations in line size D, e.g., an area in which the above-describedratio is 1:2 or more, are required to have sizes D that fall in theabove-described range of permissible variations.

The gas supply unit described in Patent Document 1 can supply a gas tothe center and edge of a wafer separately, so that it is possible tomake the depositing gas feed rate per unit area greater at the edge ofthe wafer than in the center. However, since the flow rate of an etchinggas to be supplied to the edge of the wafer also becomes higher, even ifa film is deposited in an increased amount, the film is etched in anincreased amount. Roughly speaking, therefore, it is impossible toincrease the amount of the deposit at the edge of the wafer, and also toimprove the within-wafer distribution of line sizes.

Patent Document 1: Japanese Patent Laid-Open Publication No. 2005-723((0052)-(0054)) (U.S. Patent No. 2005-29369)

SUMMARY OF THE INVENTION

The present invention was accomplished under these circumstances. Anobject of the invention is to provide a technique for uniformlyprocessing a substrate surface in the process of processing a substrateby supplying gases to it.

The present invention is a substrate processing system comprising aprocessing vessel; a table that is placed in the processing vessel andon which a substrate will be placed; a gas supply unit set on the top ofthe processing vessel facing the table, including a center section thatcorresponds to the center portion of the substrate and has a largenumber of gas-jetting pores, and a peripheral section that correspondsto the peripheral portion of the substrate and has a large number ofgas-jetting pores; a first-gas supply means of supplying a common gas tothe center and peripheral sections of the gas supply unit at flow ratesseparately regulated; a second-gas supply means of supplying anadditional gas, in addition to the common gas, to the peripheral sectionof the gas supply unit; and a means of evacuating the processing vessel,the distance from the center of the center section of the gas supplyunit to the outermost gas-jetting pores in the center section being 53%or more of the radius of the substrate.

A preferred embodiment of the present invention is the substrateprocessing system in which the first-gas supply means has a plurality ofgas supply sources for supplying different gases, a plurality of gasessupplied from a plurality of the gas supply sources are mixed, and thegas mixture is divided into two streams and supplied as the common gasto the center and peripheral sections separately.

A preferred embodiment of the present invention is the substrateprocessing system in which the common gas contains an etching gas and agas having the property of depositing on the substrate or of protectingthe side faces of projections on the substrate, the ratio of the flowrate of the former gas to that of the latter gas in the center sectionbeing the same as said ratio in the peripheral section, and theadditional gas has the property of depositing on the substrate or ofprotecting the side faces of projections on the substrate.

A preferred embodiment of the present invention is the substrateprocessing system in which the additional gas having the property ofdepositing on the substrate is a gas of a compound containing carbon andhydrogen.

A preferred embodiment of the present invention is the substrateprocessing system in which the etching gas is for etching siliconnitride film on the substrate.

A preferred embodiment of the present invention is the substrateprocessing system in which the etching gas is for etching siliconnitride film on the substrate, and the additional gas having theproperty of protecting the side faces of projections is nitrogen gas.

A preferred embodiment of the present invention is the substrateprocessing system useful for making lines in a thin film on thesubstrate by etching.

A preferred embodiment of the present invention is the substrateprocessing system in which the pressure at which the substrate isprocessed in the processing vessel is regulated to 1.3-40 Pa.

The present invention is a gas supply unit set on a processing vessel inwhich a substrate is placed, including a center section that correspondsto the center portion of the substrate and has a large number ofgas-jetting pores, and a peripheral section that corresponds to theperipheral portion of the substrate and has a large number ofgas-jetting pores, a common gas being supplied to the center andperipheral sections of the gas supply unit at flow rates separatelyregulated, an additional gas being supplied, in addition to the commongas, to the peripheral section of the gas supply unit, the distance fromthe center of the center section of the gas supply unit to the outermostgas-jetting pores in the center section being 53% or more of the radiusof the substrate.

A preferred embodiment of the present invention is the gas supply unitin which a plurality of gases supplied from a plurality of gas supplysources for supplying different gases are mixed, and the gas mixture isdivided into two streams and supplied as the common gas to the centerand peripheral sections separately.

A preferred embodiment of the present invention is the gas supply unitin which the common gas contains an etching gas and a gas having theproperty of depositing on the substrate or of protecting the side facesof projections on the substrate, the ratio of the flow rate of theformer gas to that of the latter gas in the center section being thesame as said ratio in the peripheral section, and the additional gas hasthe property of depositing on the substrate or of protecting the sidesof projections on the substrate.

The present invention is a method of processing a substrate by the useof a substrate processing system comprising a processing vessel; a tablethat is placed in the processing vessel and on which a substrate will beplaced; a gas supply unit set on the top of the processing vessel facingthe table, including a center section that corresponds to the centerportion of the substrate and has a large number of gas-jetting pores,and a peripheral section that corresponds to the peripheral portion ofthe substrate and has a large number of gas-jetting pores; a first-gassupply means of supplying a common gas to the center and peripheralsections of the gas supply unit at flow rates separately regulated; asecond-gas supply means of supplying an additional gas, in addition tothe common gas, to the peripheral section of the gas supply unit; and ameans of evacuating the processing vessel, the method comprising thesteps of supplying to the substrate from the center and peripheralsections of the gas supply unit the common process gas that has beensupplied to the two sections by the first-gas supply means at flow ratesseparately regulated, supplying, in addition to the common process gas,the additional gas that has been supplied to the peripheral section ofthe gas supply unit by the second-gas supply means, to the substratefrom the peripheral section, and evacuating the processing vessel withthe means of evacuating the processing vessel, the distance from thecenter of the center section of the gas supply unit to the outermostgas-jetting pores in the center section being 53% or more of the radiusof the substrate.

A preferred embodiment of the present invention is the method ofsubstrate processing in which the first-gas supply means has a pluralityof gas supply sources for supplying different gases, and the step ofsupplying the common gas to the substrate from the center and peripheralsections of the gas supply unit is a step in which a plurality of gasessupplied from a plurality of the gas supply sources are mixed, and thegas mixture is divided into two streams and supplied as the common gasto the center and peripheral sections separately.

A preferred embodiment of the present invention is the method ofsubstrate processing in which the common gas contains an etching gas anda gas having the property of depositing on the substrate or ofprotecting the side faces of projections on the substrate, the ratio ofthe flow rate of the former gas to that of the latter gas in the centersection being the same as said ratio in the peripheral section, and theadditional gas has the property of depositing on the substrate or ofprotecting the side faces of projections on the substrate.

A preferred embodiment of the present invention is the method ofsubstrate processing in which the additional gas having the property ofdepositing on the substrate is a gas of a compound containing carbon andhydrogen.

A preferred embodiment of the present invention is the method ofsubstrate processing in which the etching gas is for etching siliconnitride film on the substrate.

A preferred embodiment of the present invention is the method ofsubstrate processing in which the etching gas is for etching siliconnitride film on the substrate, and the additional gas having theproperty of protecting the side faces of projections is nitrogen gas.

A preferred embodiment of the present invention is the method ofsubstrate processing for making lines in a thin film on the substrate byetching.

A preferred embodiment of the present invention is the method ofsubstrate processing in which the pressure at which the substrate isprocessed in the processing vessel is regulated to 1.3-40 Pa.

The present invention is a computer program for allowing a computer toperform a method of substrate processing, the method of substrateprocessing being for processing a substrate by the use of a substrateprocessing system comprising a processing vessel; a table that is placedin the processing vessel and on which a substrate will be placed; a gassupply unit set on the top of the processing vessel facing the table,including a center section that corresponds to the center portion of thesubstrate and has a large number of gas-jetting pores, and a peripheralsection that corresponds to the peripheral portion of the substrate andhas a large number of gas-jetting pores; a first-gas supply means ofsupplying a common gas to the center and peripheral sections of the gassupply unit at flow rates separately regulated; a second-gas supplymeans of supplying an additional gas, in addition to the common gas, tothe peripheral section of the gas supply unit; and a means of evacuatingthe processing vessel, the method comprising the steps of supplying tothe substrate from the center and peripheral sections of the gas supplyunit the common process gas that has been supplied to the two sectionsby the first-gas supply means at flow rates separately regulated,supplying, in addition to the common process gas, the additional gasthat has been supplied to the peripheral section of the gas supply unitby the second-gas supply means, to the substrate from the peripheralsection, and evacuating the processing vessel with the means ofevacuating the processing vessel, the distance from the center of thecenter section of the gas supply unit to the outermost gas-jetting poresin the center section being 53% or more of the radius of the substrate.

The present invention is a storage medium in which a computer programfor allowing a computer to perform a method of substrate processing isstored, the method of substrate processing being for processing asubstrate by the use of a substrate processing system comprising aprocessing vessel; a table that is placed in the processing vessel andon which a substrate will be placed; a gas supply unit set on the top ofthe processing vessel facing the table, including a center section thatcorresponds to the center portion of the substrate and has a largenumber of gas-jetting pores, and a peripheral section that correspondsto the peripheral portion of the substrate and has a large number ofgas-jetting pores; a first-gas supply means of supplying a common gas tothe center and peripheral sections of the gas supply unit at flow ratesseparately regulated; a second-gas supply means of supplying anadditional gas, in addition to the common gas, to the peripheral sectionof the gas supply unit; and a means of evacuating the processing vessel,the method comprising the steps of supplying to the substrate from thecenter and periphral sections of the gas supply unit the common processgas that has been supplied to the two sections by the first-gas supplymeans at flow rates separately regulated, supplying, in addition to thecommon process gas, the additional gas that has been supplied to theperipheral section of the gas supply unit by the second-gas supplymeans, to the substrate from the peripheral section, and evacuating theprocessing vessel with the means of evacuating the processing vessel,the distance from the center of the center section of the gas supplyunit to the outermost gas-jetting pores in the center section being 53%or more of the radius of the substrate.

According to the present invention, in the gas supply unit thatsupplies, to a substrate, from its center and prepheral sections havinga large number of gas-jetting pores, a common process gas separately isused, and an additional gas is further supplied to the substrate fromthe peripheral section. Moreover, the gas supply unit is partitionedinto a center section and a peripheral section at an optimized position.It is therefore possible to decrease the within-substrate non-uniformityin processing that is brought about because it is more difficult toevacuate the center portion of the substrate than the peripheralportion. It is thus possible to improve the within-substrate uniformityin processing, e.g., in etching.

For example, such a pattern as a line pattern formed, by etching, in afilm on which a material is easily deposited, such as silicon nitridefilm, is apt to be smaller in width in the peripheral portion of thefilm. The within-film uniformity in pattern width can be improved byadditionally supplying, to the peripheral portion of a film, a gashaving the property of depositing on the film or of protecting the sidefaces of non-etched portions of (protrusions on) the film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of a plasma processing system towhich a gas supply unit of the present invention is applied.

FIG. 2 is a sectional view of a processing vessel 21 in the above plasmaprocessing system 2.

FIG. 3 is a view showing an upper electrode 4 in the above plasmaprocessing system 2.

FIG. 4 (a) (b) (c) are views showing an example of the structure of awafer W in plasma processing according to the present invention.

FIG. 5 (a) (b) (c) are views showing the position of a partition 55 inExperimental Example 2.

FIG. 6 (a) (b) are views showing a model of the processing vessel 21used in Experimental Example 2.

FIG. 7 is a view showing results of simulations carried out inExperimental Example 2.

FIG. 8 is a view showing the results of simulations carried out inExperimental Example 2.

FIG. 9 (a) (b) (c) are views showing the results of simulations carriedout in Experimental Example 2.

FIG. 10 (a) (b) (c) are views showing the results of experiments carriedout in Experimental Example 3.

FIG. 11 (a) (b) are sectional views showing the structure of a wafer 100in conventional plasma processing.

BEST MODE FOR CARRYING OUT THE INVENTION

An example of the application of a gas supply unit 1 of the presentinvention will be described hereinafter with reference to FIGS. 1 to 3.A plasma processing system 2 to which a gas supply unit 1 of theinvention is applied comprises a processing vessel 21 composed of e.g.,a vacuum chamber having a closed internal space, a table 3 serving alsoas a lower electrode, set in the center of the bottom of the processingvessel 21 so that a wafer (substrate) can be placed on it, and an upperelectrode 4 that is a part of a shower head set above and in parallelwith the table 3.

The processing vessel 21 has an exhaust hole 22 in its bottom, and thisexhaust hole 22 communicates with an evacuation system 23, a means ofevacuating the processing vessel 21, via an exhaust pipe 24. Theevacuation system 23 is provided with a pressure regulator not shown inthe figure. Owing to the pressure regulator, the evacuation system 23evacuates the processing vessel 21 to the desired degree of vacuum inresponse to signals from a controller 2A that will be described laterand keeps the processing vessel 21 at this degree of evacuation. Theprocessing vessel 21 has, in its sidewall, a gate 25 through which awafer W is carried in or out, and this gate 25 can be opened or closedby operating a gate valve 26. Annular permanent magnets 27, 28 are putaround the periphery of the processing vessel 21 in positions above andbelow the gate 25, respectively.

A deposit shield is laid on the inner wall of the processing vessel 21so that the inner wall is held at a high temperature, e.g., 60° C. ormore, to prevent such a material as fluorocarbon from depositing on it.The deposit shield, however, is omitted from the figure.

The table 3 is composed of a support 32 made of e.g., aluminum, anelectrostatic chuck 34, a first ring 39 made from an insulator,surrounding the electrostatic chuck 34 with a slight gap between them,and a second ring 40 made from an electrically conductive material,which is placed on the upper face of the first ring 39 and acts tospread horizontally a plasma produced above the wafer W. Theelectrostatic chuck 34 has through holes 34 a, which are necessary toelevate the wafer W, as will be described later. Further, a high-voltageD.C. power supply 35 is connected to the electrostatic chuck 34, and theelectrostatic chuck 34 electrostatically adsorbs a wafer W when power issupplied by the high-voltage D.C. power supply 35.

To the sidewall of the table 3, an annular exhaust ring 24 a serving asan exhaust buffer is attached so that it fills up the annular gapbetween the table 3 and the inner wall of the processing vessel 21. Thisexhaust ring 24 a is for making the circumferential rate of exhaustuniform, thereby making the rate of exhaust from the circumference of awafer W placed on the table 3 uniform.

To the support 32 of the table 3 is connected an RF generator 31 forgenerating a high-frequency wave of e.g., 13.56 MHz, via a condenser Cand a coil L. The RF generator 31 is for producing plasmas from processgases. It is connected to a controller 2A, which will be describedlater, and electric power to be supplied to the RF generator 31 iscontrolled according to control signals from the controller 2A. The RFgenerator 31 and the table 3 constitute a means of generating plasmas.

Inside the table 3 is an elevating member 5 of delivering a wafer W fromthe table 3 to a carrier arm that is present outside the processingvessel 21, though not shown in the figure, and vice versa. The elevatingmember 5 is composed of a plurality of, e.g., three, elevating pins 5 apenetrating the table 3 and the bottom of the processing vessel 21, adriving mechanism 5 b for driving these elevating pins 5 a, and soforth. By means of the driving mechanism 5 b, the tips of the elevatingpins 5 a are raised above and downed into the through holes 34 a made inthe electrostatic chuck 34.

The upper electrode 4 and a cover 52 placed on it constitute a nearlydisc-shaped gas shower head, a gas supply unit 1. The cover 52 isgrounded. The space facing the table 3, enclosed by the upper electrode4 and the cover 52 is partitioned by an annular partition 55 into acenter section 53 a corresponding to the center portion Wa of a wafer Wand an edge section (peripheral section) 53 b corresponding to the edgeportion (peripheral portion) Wb of the wafer W. The center section 53 aand the edge section (peripheral section) 53 b have a gas supply port 54a and a gas supply port 54 b, respectively, so that a first gas and asecond gas, which will be described later, pass through the respectiveports. Although only one gas supply port 54 b is made in the cover 52 inthis example, two or more gas supply ports 54 b may also becircumferentially made in the cover 52 at regular intervals.

As shown in FIG. 3, the upper electrode 4 has a large number ofgas-jetting pores 51 for dispersively feeding a process gas to a waferW. These gas-jetting pores 51 are made in e.g., seven circular rowsconcentric with the wafer W so that 8, 12, 20, 28, 36, 42, and 50 poresare on the circumferences of concentric circles with radii of 20 mm, 40mm, 60 mm, 80 mm, 100 mm, 120 mm, and 140 mm, respectively. Thesegas-jetting pores 51 are grouped by the above-described partition 55into the gas-jetting pores 51 communicating with the nearly circularcenter section 53 a, and the gas-jetting pores 51 communicating with thenearly annular edge section 53 b.

In this example, the partition 55 is positioned so that the distancefrom the center of the center section 53 a to the outermost row of thegas-jetting pores 51 in the center section 53 a (the radius RO of theoutermost circle of the gas-jetting pores 51 in the center section 53 a)is 80% of the radius of the wafer W. Namely, in processing a wafer Wwith a diameter of 300 mm, the partition 55 is placed in a position 130mm apart from the center of the upper electrode 4; a first gas issupplied to the center portion of the wafer W from the gas-jetting pores51 on the circumferences of six circles on the center side, and a secondgas, to the edge portion of the wafer from the gas-jetting pores 51 onthe circumference of the remaining one circle on the edge side. In thiscase, the above-described radius RO is 120 mm, so that the percentage ofthe radius RO to the radius of the wafer W is 80%. By altering theposition of the partition 55, the center section 53 a and the edgesection 53 b can be varied in size. This means that it is possible tovary the area of the center portion of a wafer W to which the first gasis supplied, and that of the edge portion of the wafer W to which thesecond gas is supplied.

Although the gas-jetting pores 51 are disposed concentrically with thewafer W in this example, they may also be disposed in a grid or zigzagpattern.

The space between the upper electrode 4 and the cover 52 is partitionedinto upper and lower sections by a disc-shaped diffuser 56. The diffuser56 has gas-flowing pores 57 made, for example, in circular rowsconcentric with a wafer W, corresponding to the concentric circles ofthe gas-jetting pores 51. The positions of the gas-flowing pores 57 areshifted from those of the gas-jetting pores 51 by e.g., 10 mm so thatthe stream of a gas flowing in the space above the diffuser 56 isdiffused, thereby making the distribution of the gas to be jetted fromthe center section 53 a and that of the gas to be jetted from the edgesection 53 b uniform. Further, the diffuser 56 has projections on it inthe positions corresponding to the gas supply ports 54 a, 54 b, so thata gas supplied to the center section 53 a and a gas supplied to the edgesection 53 b are dispersed. The above-described partition 55 is dividedinto upper and lower parts by the diffuser 56, but these two partsextend upwardly and downwardly from one point on the diffuser 56 andconstitute the partition 55.

As mentioned above, the gas supply ports 54 a, 54 b are made in theupper surface of the cover 52 so that they communicate with the centersection 53 a and the edge section 53 b, respectively. The gas supplyports 54 a, 54 b communicate, via gas feed pipes 42 a, 42 b, withpressure regulators 41 a, 41 b that are means of regulating the flowrates of gases to be supplied to the center section 53 a and the edgesection 53 b, respectively. On the upstream side of the pressureregulators 41 a, 41 b, the gas feed pipes 42 a, 42 b join a gas feedpipe 42. The gas feed pipe 42 is branched, on its upstream side, intofour branch pipes 42A to 42D. The branch pipes 42A to 42D communicatewith gas supply sources 45A to 45D, which constitute a gas supply sourceM, via valves 43A to 43D and flow rate controllers 44A to 44D,respectively. A common gas is supplied from the gas source M to thepressure regulators 41 a, 41 b, and a controller 2A, which will bedescribed later, controls the pressures of the pressure regulators 41 a,41 b to regulate separately the flow rate of the gas to be supplied tothe center section 53 a and that of the gas to be supplied to the edgesection 53 b. The common gas herein means that, in the case where a gasmixture of two or more process gases is supplied to the center section53 a and to the edge section 53 b, the gas mixture to be supplied to thecenter section 53 a and the one to be supplied to the edge section 53 bare the same in the ratio at which the process gases are mixed. Forexample, this means that an etching gas and a depositing gas that aresupplied to the center section 53 a and the ones that are supplied tothe edge section 53 b are identical in the ratio of the flow rate of theetching gas to that of the depositing gas.

The gas source M, the flow rate controllers 44A to 44D, the valves 43Ato 43D, the branch pipes 42A to 42D, the gas feed pipe 42, the pressureregulator 41 a, and the gas feed pipe 42 a constitute a means forsupplying a common gas to the center section 53 a. On the other hand,the gas source M, the flow rate controllers 44A to 44D, the valves 43Ato 43D, the branch pipes 42A to 42D, the gas feed pipe 42, the pressureregulator 41 b, and the gas feed pipe 42 b constitute a means forsupplying a common gas to the edge section 53 b. These means forsupplying a common gas to the center section 53 a and the edge section53 b constitute a first-gas supply means 40A.

On the other hand, a gas feed pipe 42 c is connected to theabove-described gas feed pipe 42 b at a point between the gas feed port54 b and the pressure regulator 41 b. The gas feed pipe 42 c isbranched, on its upstream side, into three branch pipes 42E, 42F, 42G,which communicate with gas supply sources 45E, 45F constituting a gassource A and also with a gas supply source 45G, via valves 43E, 43F, 43Gand flow rate controllers 44E, 44F, 44G, respectively. A gas suppliedfrom the gas source A is added to the gas that has been supplied fromthe gas source M and is flowing in the above-described gas feed pipe 42b. This gas has the property of protecting openings 77 in a photoresistmask 71, which will be described later, as well as the inner walls ofcavities 78 formed in films lying under the photoresist mask 71. The gassource A, the flow rate controllers 44E, 44F, the valves 43E, 43F, thebranch pipes 42E, 42F, and the gas feed pipe 42 c constitute a means forsupplying an additional gas to the edge section 53 b. The means forsupplying an additional gas to the edge section 53 b is a second-gassupply means 40B.

The valves 43A to 43G and the flow rate controllers 44A to 44Gconstitute a gas supply system 46, with which the flow rates of gasessupplied from the gas supply sources 45A to 45G, the supply and stoppageof these gasses, and the pressures of gases flowing in the gas feedpipes 42 a, 42 b are controlled according to control signals from thecontroller 2A, which will be described later. Namely, as will bedescribed later, in order to decrease variations in wafer W processing,the flow rate of a second gas to be supplied to the edge portion of thewafer W and that of a first gas to be supplied to the center portion ofthe wafer W are regulated, and a gas from the gas source A is added tothe second gas. A gas that flows in the gas feed pipe 42 a and a gasthat flows in the gas feed pipe 42 b are the first gas and the secondgas, respectively.

This plasma processing system 2 is provided with the controller 2Acomposed of a computer, for example. The controller 2A comprises aprogram, a memory, and a data processor composed of a CPU. The programcontains commands to the controller 2A to send control signals tovarious parts of the plasma processing system 2 to carry out the stepsthat will be described later, thereby plasma-processing a wafer W. Thememory has an area in which the process parameters such as processpressure, process time, gas flow rate, and power value are written, andwhen the CPU executes each command in the program, these processparameters are read out, and control signals corresponding to theparameter values are sent to the respective parts of the plasmaprocessing system 2. This program (including programs concerning theinput operation and display of the process parameters) is stored in amemory area 2B of a computer storage medium such as a flexible disc, acompact disc, an MO (magneto-optical disc), or a hard disc (HD), and isinstalled in the controller 2A.

Next, an embodiment of the present invention, using the plasmaprocessing system 2 to which the gas supply unit 1 is applied, will bedescribed. The gate valve 26 is first opened, and a wafer W with adiameter of 300 mm (12 inches) is carried in the processing vessel 21through the gate 25 by a wafer-transferring mechanism that is not shownin the figure. After placing the wafer W on the table 3 by means of theelevating member 5, the table 3 is allowed to adsorb the wafer Welectrostatically. The wafer-transferring mechanism is then withdrawnfrom the processing vessel 21 and the gate valve 26 is closed.Subsequently, by supplying a backside gas from a gas line 38, the waferW is controlled to a predetermined temperature. Thereafter, thefollowing steps are carried out.

The structure of the surface of a wafer W is shown in FIG. 4(a).Polycrystalline Si film 76 is deposited on a transistor gate oxide filmthat is not shown in the figure, and on this film 76, W-Si(tungsten-silicon compound) film 75, SiN film 74, SiO₂ film 73, anantireflection film 72, and a photoresist mask 71 with openings 77 aredeposited in the order mentioned. The W-Si film 75 and thepolycrystalline Si film 76 are gate electrode materials, and the SiNfilm 74 serves as a hard mask when the gate electrode materials areetched into a line pattern to form a gate electrode.

(Step 1: Step of Etching Antireflection Film 72)

The processing vessel 21 is evacuated by the evacuation system 23through the exhaust pipe 24 and is held at a predetermined degree ofvacuum of e.g., 15.3 Pa (115 mTorr). For example, CF₄ gas, Ar gas, andO₂ gas are then supplied from the gas source M at flow rates of 120sccm, 420 sccm, and 10 sccm, respectively. The pressure regulators 41 a,41 b are controlled by the controller 2A so that the ratio of thepressure (flow rate) of the gases to be supplied to the gas feed pipe 42a to the pressure of the gases to be supplied to the gas feed pipe 42 bbecomes 45:55, for example.

Subsequently, a high-frequency wave with a frequency of 13.56 MHz and apower of 800 W is applied to the table 3, thereby producing a plasmafrom a gas mixture of the above-described gases. This plasma becomesdense when kept in the space above the wafer W by the magnetic fieldproduced by the permanent magnets 27, 28.

This plasma contains active species of compounds consisting of hydrogenand fluorine, and when the antireflection film 72 is exposed to anatmosphere containing these active species, atoms present in this filmreact with the active species to give compounds, whereby theantireflection film 72 is etched.

(Step 2: Step of Etching SiO₂ Film 73)

Thereafter, the processing vessel 21 is evacuated by the evacuationsystem 23 through the exhaust pipe 24 and is held at a predetermineddegree of vacuum of e.g., 13.3 Pa (100 mTorr). For example, CH₂F₂ gas,CF₄ gas, and Ar gas are then supplied from the gas source M at flowrates of 15 sccm, 100 sccm, and 600 sccm, respectively. The pressureregulators 41 a, 41 b are controlled by the controller 2A so that theratio of the pressure (flow rate) of the gases to be supplied to the gasfeed pipe 42 a to the pressure of the gases to be supplied to the gasfeed pipe 42 b becomes 45:55, for example.

Subsequently, a high-frequency wave with a frequency of 13.56 MHz and apower of 1200 W is applied to the table 3, thereby generating plasmafrom a gas mixture of the above-described gases. This plasma becomesdense when kept in the space above the wafer W by the magnetic fieldproduced by the permanent magnets 27, 28.

When the SiO₂ film 73 is exposed to active species of compoundsconsisting of carbon and fluorine, contained in the plasma, atomspresent in this film react with the active species to give compounds,whereby the SiO₂ film 73 is etched to create cavities 78 in the film, asshown in FIG. 4(b).

(Step 3: Step of Etching SiN Film 74)

The processing vessel 21 is evacuated by the evacuation system 23through the exhaust pipe 24 and is held at a predetermined degree ofvacuum of e.g., 18.7 Pa (140 mTorr). For example, CH₂F₂ gas, CF₄ gas, Argas, and O₂ gas are then supplied from the gas source M at flow rates of15 sccm, 80 sccm, 150 sccm, and 21 sccm, respectively. The pressureregulators 41 a, 41 b are controlled by the controller 2A so that theratio of the pressure (flow rate) of the gases to be supplied to the gasfeed pipe 42 a to the pressure of the gases to be supplied to the gasfeed pipe 42 b (the ratio of the pressure of the gases to be supplied tothe center section 53 a to the pressure of the gases to be supplied tothe edge section 53 b) becomes 45:55, for example. And CH₂F₂ gas isfurther supplied from the gas source A at a flow rate of 5 sccm, forexample.

Subsequently, a second high-frequency wave with a frequency of 13.56 MHzand a power of 700 W is applied to the table 3, thereby producing aplasma from the gases supplied to the processing vessel 21 from the gassources M and A. This plasma becomes dense when kept in the space abovethe wafer W by the magnetic field produced by the permanent magnets 27,28.

In this example, CF₄ gas and O₂ gas are etching gases, and CH₂F₂ gas isa depositing gas. In the plasma of these gases, the active speciesproduced by the dissociation of CF₄ gas and oxygen active species act toetch the SiN film 74 to form therein cavities 78 (grooves), while theactive species produced by the dissociation of CH₂F₂ gas deposit on theinner walls of the cavities 78. Owing to the actions of the two types ofgases, the etching process progresses while restraining the increase inthe openings of the cavities, as shown in FIG. 4(c). O₂ gas is forcreating plasma with which the SiN film 74 is etched vertically to thewafer W.

In this process, since the processing vessel 21 is evacuated by theevacuation system 23, the gases supplied to the wafer W from the upperelectrode 4 is more easily exhausted from the edge portion of the waferW than from the center portion. In order to make up for this, the ratioof the flow rate of the gases to be supplied to the center section 53 ato the flow rate of the gases to be supplied to the edge section 53 b isset to 45:55, thereby making the gas flow rate per unit area greater inthe edge section 53 b than in the center section 53 b. Further, as canbe understood from the following Examples, the boundary between thecenter section 53 a and the edge section 53 b to which gases aresupplied independently is optimized, and moreover, with considerationfor the fact that gas pressure differences greatly affect the amount ofa film to be deposited on the inner walls of cavities in SiN film 74,the area to which gases are supplied was divided into the center section53 a and the edge section 53 b. Furthermore, since the gas pressure inthe edge portion of a wafer W is low, CH₂F₂ gas, a depositing gas, issupplied from the edge section 53 b as an additional gas. Consequently,the etching process progresses without making the sizes of thenon-etched. portions 79 in the center portion of a wafer W greater thanthe sizes of the non-etched portions 79 in the edge portion of the waferW.

Thereafter, the photoresist mask 71 is removed by ashing, and aftercleaning the wafer W, the W-Si film 75 and the polycrystalline Si film76 are etched with the use of the SiO₂ film 73 and the SiN film 74 as amask.

According to the above-described embodiment, the partition 55 useful forsupplying gases to the center and edge portions of a wafer W separatelyis placed in an optimum position, and CH₂F₂ gas having the property ofdepositing on SiN film 74 is supplied to the edge portion 53 b. As thefollowing Examples show, therefore, lines uniform in width can be madenot only in a densely-patterned area of the wafer W in which the ratioof metallic lines to insulation layers between them is about 1:1, butalso in a non-densely-patterned area of the wafer W in which the aboveratio is 1:2 or more.

In this example, CH₂F₂ gas is used as the gas from the gas source A tobe added to the second gas, having the property of protecting the sides(side faces) of non-etched portions 79. The gas from the gas source A isnot limited to CH₂F₂ gas, and a gas having the property of protectingthe sides of non-etched portions 79, such as N₂ gas, or a gas containingcarbon and hydrocarbon, having the property of depositing on the sidesof the non-etched portions 79, such as CH₃F gas, may also be used.

In the step of etching the SiN film 74, the wafer W generates N₂ gas asa reaction product, but this gas is exhausted by the evacuation system23. The N₂ gas concentration, therefore, is lower in the edge portion Wbof the wafer W than in the center portion Wa. With consideration forthis fact, N₂ gas is supplied to the edge portion Wb of the wafer W fromthe gas source A in order to make the N₂ gas distribution on the wafer Wsurface uniform. Consequently, the non-uniformity of the distribution ofprocess gases supplied from the gas source M to the wafer W via thecenter section 53 a and the edge section 53 b can be decreased, and thenon-etched portions 79 of the wafer W thus become uniform in size. SinceN₂ gas produces no plasma species having an influence on SiN film 74 anddoes not adversely affect the plasma-processing of a wafer W, it may beused as a gas having the property of protecting the (side faces) ofnon-etched portions 79, as mentioned above.

On the other hand, the radius RO of the outermost circle of thegas-jetting pores 51 in the center section 53 a is not limited to 80% ofthe radius of a wafer W. It can be known from the following Examplesthat the same effects can be obtained as long as the radius RO is notless than 53% of the radius of a wafer W. For example, when the radiusRO is set to 53% of the radius of a wafer W with a diameter of 300 mm,the partition 55 is placed between the outer third and fourth circles ofthe gas-jetting pores 51.

The gas supply unit 1 of the present invention can make it possible toprocess a wafer uniformly because it is partitioned into the centersection 53 a and the edge section 53 b in the above-describedproportion, and an additional gas is supplied to a wafer from the edgesection 53 b. Therefore, when the present invention is applied also toSiN film 74, it is preferable to set the proportion of the centersection 53 a to the edge section 53 b to a percentage in theabove-described range. However, as far as SiN film 74 is concerned, itis not necessary that the proportion of the center section 53 a to theedge section 53 b be 53% or more, and even the novel technique alone,which a gas having the property of depositing on SiN film or ofprotecting the sides of non-etched portions of SiN film is supplied tothe edge section 53 b, can produce satisfactory effects as compared withconventional techniques.

In the case where a line pattern is made in a wafer W, a gas supplied tothe wafer W flows along the pattern in the wafer, so that the gasdistribution on the wafer W surface tends to be non-uniform as comparedwith the case where holes are made in a wafer W. However, as thefollowing Examples show, even when a line pattern is made in a wafer Wby etching, within-wafer variations in line size can be made small bythe use of the plasma processing system 2 to which the gas supply unit 1of the present invention is applied.

A system in which RF energy for making process gases into a plasma andanother RF energy for drawing the plasma to a wafer W are applied to theupper electrode 4 and the table 3, respectively, may also be used as theplasma processing system 2 for use in the present invention. Further, inthe above-described example, the plasma is made dense by keeping it inthe space above a wafer W by using the permanent magnets 27, 28, but itis not necessary to provide the permanent magnets 27, 28.

The gas supply unit 1 of the present invention can be applied not onlyto a plasma processing system 2, but also to a system for processing asubstrate by supplying a process gas to the substrate, such as a CVDsystem.

Next, experiments and simulations that were carried out in order to findthe optimum position of the outermost circle of the gas-jetting pores 51communicating with the center section 53 a of the upper electrode in thegas supply unit 1 of the present invention will be describedhereinafter. In the following Experimental Examples, a plasma processingsystem 2 having the structure shown in FIGS. 1 to 3 was used to processa wafer W with a plasma. To simplify the process, the processing vessel21 vertically cut up into four, as shown in FIG. 6, was used as a modelin the simulations.

Experiments were carried out by placing the partition 55 in one of thefollowing three positions, as shown in FIG. 5: the position at which thegas-jetting pores 51 made in the upper electrode 4 in seven concentriccircular rows are divided into four inner and three outer circles of thegas jetting pores 51 (FIG. 5(a)); the position at which the gas-jettingpores 51 are divided into five inner and two outer circles of thegas-jetting pores 51 (FIG. 5(b)); and the position at which thegas-jetting pores 51 are divided into six inner and one outer circles ofthe gas-jetting pores 51 (FIG. 5(c)). Namely, the position of thepartition 55 was set so that the radius of the outermost circle of thegas-jetting pores 51 communicating with the center section 53 a was 53%of the radius of a wafer W (distance L from the center of the upperelectrode 4 to the partition 55: 90 mm); that the radius of theoutermost circle of the gas-jetting pores 51 communicating with thecenter section 53 a was 67% of the radius of a wafer W (distance L: 110mm); or that the radius of the outermost circle of the gas-jetting pores51 communicating with the center section 53 a was 80% of the radius of awafer W (distance L: 130 mm).

Further, in order to obtain the data on SiN film 74, a wafer W havingthe structure shown in FIG. 4(a) was made into the state as shown inFIG. 4(b) by etching the antireflection film 72 and the SiO₂ film 73under the following process conditions, and was used in the followingExperimental Examples 1 and 3.

(Etching of Antireflection Film 72)

Frequency of high-frequency wave: 13.56 MHz

Power of high-frequency wave: 800 W

Process pressure: 15.3 Pa (115 mTorr)

Process gases (gas source M): CF₄/Ar/O_(2=120/420/10) sccm

Pressures of pressure regulators:

-   -   pressure regulator 41 a/pressure regulator 41 b=45/55

The partition 55 was placed in such a position that the distance L wasequal to 130 mm.

(Etching of SiO₂ Film 73)

Frequency of high-frequency wave: 13.56 MHz

Power of high-frequency wave: 1200 W

Process pressure: 13.3 Pa (100 mTorr)

Process gases (gas source M): CH₂F₂/CF₄/Ar=15/100/600 sccm

Pressures of pressure regulators:

-   -   pressure regulator 41 a/pressure regulator 41 b=45/55

The partition 55 was placed in the same position as the above.

EXPERIMENTAL EXAMPLE 1 Etching Rate

Prior to carrying out simulations, an experiment for estimating theamount of a gas to be generated from the wafer W in the step of etchingthe SiN film 74 was carried in order to determine more practicalconditions. The SiN film 74 was etched under the following processconditions.

(Etching of Sin Film 74)

Frequency of high-frequency wave: 13.56 MHz

Power of high-frequency wave: 700 W

Process pressure: 18.7 Pa (140 mTorr)

Process gases (gas source M):

-   -   CH₂F₂/CF₄/Ar/O₂=15/80/150/21 sccm

Process gas (gas source A): CH₂F₂₌₅ sccm

Pressures of pressure regulators:

-   -   pressure regulator 41 a/pressure regulator 41 b=    -   55/45 (distance L=90 mm),    -   1/1 (distance L=110 mm), and    -   45/55 (distance L=130 mm)        Results of Experiments

The etching rates of the SiN film 74 determined in the above experimentsare shown in Table 1. TABLE 1 Distance L (mm) 90 110 130 Etching Rate180.4 181.3 180.9 (nm) Standard 1.8 1.4 1.9 Deviation (%)

From the data shown in Table 1, it was found that almost the sameetching rate was obtained independently of the percentage of the radiusof the outermost circle of the gas-jetting pores 51 communicating withthe center section 53 a to the radius of the wafer W (regardless of thedistance L). Further, from the composition of the SiN film 74, as wellas the type and flow rate of the gases to be supplied to the wafer W, itis expected that CN gas and SiF₄ gas will be mainly generated in thestep of etching the SiN film 74. It is also expected from the etchingrate of the SiN film 74 that the rate of gas generation will be 0.001g/sec.

EXPERIMENTAL EXAMPLE 2 Simulation

The gas distribution in the processing vessel 21 was simulated with theuse of a fluid analysis soft, Fluent Vers. 6.2.16, manufactured byFLUENT Corp. The simulation was carried out on the assumption that gasesare compressive fluids and that their flows are laminar. Further,calculations were made on the assumption that a gas causes slips invelocity and jumps in temperature on a solid surface such as a wafer Wor upper electrode 4 surface.

The distance L from the center of the upper electrode 4 to the partition55 was, as shown in FIG. 5, made 90 mm, 110 mm, or 130 mm so that theradius of the outermost circle of the gas-jetting pores 51 communicatingwith the center section 53 a was 53%, 67%, or 80% of the radius of thewafer W, respectively.

The simulations were carried out under the same process conditions as inthe above-described Experimental Example 1, except that the processpressure was set to the following three levels and that the gas flowrates were changed to the values as shown in Table 2.

(Process Conditions in Simulation)

Process pressure: 8 Pa (60 mTorr), 13.3 Pa (100 mTorr), or 18.7 Pa (140mTorr) TABLE 2 Distance L 90 mm 110 mm 130 mm First Second First SecondFirst Second gas gas gas gas gas gas Gas Gas CH2F2 4.5 10.5 7.4 7.6 10.24.8 flowrate source CF4 24 56 40 40 54 26 (sccm) M Ar 45 105 74 76 10248 O2 6.4 14.6 10.4 10.6 14.3 6.7 Gas CH2F2 0 5 0 5 0 5 source A total79.9 191.1 131.8 139.2 180.5 90.5 The number of 68 128 104 92 146 50gas-jetting pores 51

The upper electrode 4 used had gas-jetting pores 51 made in sixconcentric circular rows; the number of the gas-jetting pores 51 in thefirst (innermost) to sixth (outermost) row was 8, 12, 20, 36, 44, and48, respectively.

The number of the gas-jetting pores 51 in each row is also shown inTable 2.

In order to know the distribution of the first gas and that of thesecond gas separately, simulations were carried out by singly supplyingthe first and second gases. Further, with respect also to the gases fromthe gas sources M and A, contained in the second gas, simulations werecarried out by singly supplying the gases, or by supplying, along withthe first gas, one of the gases as the second gas. Simulation on thereaction product gas was also carried out.

Assuming that the wafer W will generate 25 wt. % of CN gas and 75 wt. %of SiF₄ gas while the wafer W is etched, and expecting from the etchingrates obtained in Experimental Example 1 that the gases will be producedat a rate of 0.001 g/second, calculations were made. It was also assumedthat the first gas, the second gas, and the gas generated from the waferW were uniform mixtures of constituent gases

Furthermore, the temperatures of various parts of the processing vessel21 were measured and were used for the simulations. The temperaturesmeasured are shown in Table 3. TABLE 3 Temperature (° C.) Second Ring 40115 Wafer W 70 Upper Electrode 4 60 Inner Wall of Processing Chamber 2160 Sidewall of Table 3 115 Electrostatic Chuck 34 60

The physical properties of the gases used in the simulations are shownin Table 4. TABLE 4 Thermal Gas Density Specific conductivity(w/Coefficient Molar species (kg/m3) heat(J/(kgK)) (mK)) of viscosityweight CH2F2 The law 116.492 + The The 0.052 of ideal 2.58851 × T +kinematical kinematical gas was 0.0019696 × T2 theory was theory wasapplied applied applied CF4 The law 158.858 − The The 0.088 of ideal2.30219 × T − kinematical kinematical gas was 0.00184652 × T2 theory wastheory was applied applied applied Ar The law 520.64 The The 0.04 ofideal kinematical kinematical gas was theory was theory was appliedapplied applied O2 The law 878.491 − The The 0.032 of ideal 0.000115007× T + kinematical kinematical gas was 0.000545659 × T2 theory was theorywas applied applied applied CN The law 1043 The The 0.026 of idealkinematical kinematical gas was theory was theory was applied appliedapplied SiF4 The law 257.81 + The The 0.1041 of ideal 2.07249 × T −kinematical kinematical gas was 0.00211759 × T2 theory was theory wasapplied applied applied

RESULTS OF EXPERIMENTS

The gas concentration distributions in the processing vessel 21 at 18.7Pa (140 mTorr), obtained from the simulations, are shown in FIGS. 7 and8. FIGS. 7 and 8 are sectional views, taken along line A-A′ in FIG.6(b), showing the gas concentration distributions in the processingvessel 21.

The simulations have demonstrated the following: when a gas from the gassource M is supplied as the second gas to the first gas, the gasdistribution on the wafer W surface becomes uniform, and if a gas fromthe gas source A is added to the second gas, the gas distributionbecomes more uniform. Moreover, it was confirmed that, as the radius ofthe outermost circle of the gas-jetting pores 51 communicating with thecenter section 53 a increases (as the distance L increases to 130 mm),the uniformity of gas concentration distribution on the wafer W surfaceincreases.

The above-described results obtained at 18.7 Pa (140 mTorr) and theresults obtained at 8 Pa (60 mTorr) are graphed in FIG. 9, in which gaspartial pressure is plotted vertically and distance L horizontally. Thepartial pressures plotted in the graphs were values measured at a point0.5 mm above the wafer W surface.

The above-described results were confirmed by the graphs in FIG. 9.Further, it was found from FIG. 9(a) that even when no additional gas issupplied from the gas source A, as the radius of the outermost circle ofthe gas-jetting pores 51 communicating with the center section 53 aincreases (as the distance L increases to 130 mm), the influence of thesecond gas on the center portion of the wafer W lessens, i.e., theinclination of the graph in the edge portion of the wafer W becomessharper. It was also found from FIG. 9(c) that even when no additionalgas from the gas source A is supplied, the gas partial pressuredistribution becomes uniform.

It was observed that the tendency in the above-described results wasindependent of pressure. It was, however, found that the non-uniformityof gas distribution decreases as pressure decreases. Further, althoughnot shown in FIG. 9, simulation was carried out also at 13.3 Pa (100mTorr). The results of this simulation were intermediate between theresults obtained at 18.7 Pa (140 mTorr) and those obtained at 8 Pa (60mTorr).

EXPERIMENTAL EXAMPLE 3 Verification of Simulations

Experiments were carried out in order to verify the results of thesimulations carried out in Experimental Example 2. In the experiments,the same processing process as in Experimental Example 1 was carriedout, and the wafer W in the state as shown in FIG. 4(b) was etched. Theprocess conditions used were the same as in Experimental Example 2,except for the following conditions.

(Process Conditions)

Distance L from the center of the upper electrode 4

-   -   to the partition 55: as described above

Process pressure: 18.7 Pa (140 mTorr)

Process gases (gas source M): as described above

Process gas (gas source A): as described above

EXPERIMENTAL EXAMPLE 3-1

The radius of the outermost circle of the gas-jetting pores 51communicating with the center section 53 a was made 80% of the radius ofthe wafer W (the distance L was made 130 mm). The flow rates of theprocess gases from the gas sources M and A were made as shown in thecolumn “distance L=130 mm” of Table 2.

EXPERIMENTAL EXAMPLE 3-2

The radius of the outermost circle of the gas-jetting pores 51communicating with the center section 53 a was made 53% of the radius ofthe wafer W (the distance L was made 90 mm). The flow rates of theprocess gases from the gas sources M and A were made as shown in thecolumn “distance L=90 mm” of Table 2.

EXPERIMENTAL EXAMPLE 3-3 Comparative Example

Experiments were carried out under the same conditions as inExperimental Example 3-2, except that the flow rate of the gas from thegas source A was made zero.

RESULTS OF EXPERIMENTS

In the densely- and non-densely-patterned areas of the wafer W, the sizeD1 of the non-etched portions of the photoresist mask 71 and the size D2of the non-etched portions of the SiN film 74 (see FIG. 4) were measuredin the X- and Y-directions of the wafer W, and ΔD (ΔD=D2−D1) wascalculated and graphed in FIG. 10. As a result, it was found that, asthe radius of the outermost circle of the gas-jetting pores 51communicating with the center section 53 a increases, the gasdistribution becomes uniform, and variations in AD decrease not only inthe densely-patterned area of the wafer W but also in thenon-densely-patterned area. It was also found that the addition of thegas from the gas source A to the second gas improved the uniformity ofΔD. In Experimental Example 3-2, an abrupt rise in ΔD, which isconsidered to be the influence of the second gas, was observed at pointsabout ±100 mm distant from the center of the wafer W, as shown inExperimental Example 2. However, the results obtained in ExperimentalExample 3-2 were better than those obtained in Experimental Example 3-3(Comparative Example).

1. A substrate processing system comprising: a processing vessel, atable that is placed in the processing vessel and on which a substratewill be placed, a gas supply unit set on the top of the processingvessel facing the table, including a center section that corresponds tothe center portion of the substrate and has a large number ofgas-jetting pores, and a peripheral section that corresponds to theperipheral portion of the substrate and has a large number ofgas-jetting pores, a first-gas supply means of supplying a common gas tothe center and peripheral sections of the gas supply unit at flow ratesseparately regulated, a second-gas supply means of supplying anadditional gas, in addition to the common gas, to the peripheral sectionof the gas supply unit, and a means of evacuating the processing vessel,the distance from the center of the center section of the gas supplyunit to the outermost gas-jetting pores in the center section being 53%or more of the radius of the substrate.
 2. The substrate processingsystem according to claim 1, wherein the first-gas supply means has aplurality of gas supply sources for supplying different gases, aplurality of gases supplied from a plurality of the gas supply sourcesare mixed, and the gas mixture is divided into two streams and suppliedas the common gas to the center and peripheral sections separately. 3.The substrate processing system according to claim 1, wherein the commongas contains an etching gas and a gas having the property of depositingon the substrate or of protecting the side faces of projections on thesubstrate, the ratio of the flow rate of the former gas to that of thelatter gas in the center section being the same as said ratio in theperipheral section, and the additional gas has the property ofdepositing on the substrate or of protecting the side faces ofprojections on the substrate.
 4. The substrate processing systemaccording to claim 3, wherein the additional gas having the property ofdepositing on the substrate is a gas of a compound containing carbon andhydrogen.
 5. The substrate processing system according to claim 4,wherein the etching gas is for etching silicon nitride film on thesubstrate.
 6. The substrate processing system according to claim 3,wherein the etching gas is for etching silicon nitride film on thesubstrate, and the additional gas having the property of protecting theside faces of projections is nitrogen gas.
 7. The substrate processingsystem according to claim 3, useful for making lines in a thin film onthe substrate by etching.
 8. The substrate processing system accordingto claim 1, wherein the pressure at which the substrate is processed inthe processing vessel is regulated to 1.3-40 Pa.
 9. A gas supply unitset on a processing vessel in which a substrate is placed, including acenter section that corresponds to the center portion of the substrateand has a large number of gas-jetting pores, and a peripheral sectionthat corresponds to the peripheral portion of the substrate and has alarge number of gas-jetting pores, a common gas being supplied to thecenter and peripheral sections of the gas supply unit at flow ratesseparately regulated, an additional gas being supplied, in addition tothe common gas, to the peripheral section of the gas supply unit, thedistance from the center of the center section of the gas supply unit tothe outermost gas-jetting pores in the center section being 53% or moreof the radius of the substrate.
 10. The gas supply unit according toclaim 9, wherein a plurality of gases supplied from a plurality of gassupply sources for supplying different gases are mixed, and the gasmixture is divided into two streams and supplied as the common gas tothe center and peripheral sections separately.
 11. The gas supply unitaccording to claim 9, wherein the common gas contains an etching gas anda gas having the property of depositing on the substrate or ofprotecting the side faces of projections on the substrate, the ratio ofthe flow rate of the former gas to that of the latter gas in the centersection is the same as said ratio in the peripheral section, and theadditional gas has the property of depositing on the substrate or ofprotecting the sides of projections on the substrate.
 12. A method ofprocessing a substrate by the use of a substrate processing systemcomprising: a processing vessel, a table that is placed in theprocessing vessel and on which a substrate will be placed, a gas supplyunit set on the top of the processing vessel facing the table, includingof a center section that corresponds to the center portion of thesubstrate and has a large number of gas-jetting pores, and a peripheralsection that corresponds to the peripheral portion of the substrate andhas a large number of gas-jetting pores, a first-gas supply means ofsupplying a common gas to the center and peripheral sections of the gassupply unit at flow rates separately regulated, a second-gas supplymeans of supplying an additional gas, in addition to the common gas, tothe peripheral section of the gas supply unit, and a means of evacuatingthe processing vessel, the method comprising the steps of: supplying tothe substrate from the center and peripheral sections of the gas supplyunit the common process gas that has been supplied to the two sectionsby the first-gas supply means at flow rates separately regulated,supplying, in addition to the common process gas, the additional gasthat has been supplied to the peripheral section of the gas supply unitby the second-gas supply means, to the substrate from the peripheralsection, and evacuating the processing vessel with the means ofevacuating the processing vessel, the distance from the center of thecenter section of the gas supply unit to the outermost gas-jetting poresin the center section being 53% or more of the radius of the substrate.13. The method of substrate processing according to claim 12, whereinthe first-gas supply means has a plurality of gas supply sources forsupplying different gases, and the step of supplying the common gas tothe center and peripheral sections of the gas supply unit is a step inwhich a plurality of gases supplied from a plurality of the gas supplysources are mixed, and the gas mixture is divided into two streams andsupplied as the common gas to the center and peripheral sectionsseparately.
 14. The method of substrate processing according to claim12, wherein the common gas contains an etching gas and a gas having theproperty of depositing on the substrate or of protecting the side facesof projections on the substrate, the ratio of the flow rate of theformer gas to that of the latter gas in the center section being thesame as said ratio in the peripheral section, and the additional gas hasthe property of depositing on the substrate or of protecting the sidefaces of projections on the substrate.
 15. The method of substrateprocessing according to claim 14, wherein the additional gas having theproperty of depositing on the substrate is a gas of a compoundcontaining carbon and hydrogen.
 16. The method of substrate processingaccording to claim 15, wherein the etching gas is for etching siliconnitride film on the substrate.
 17. The method of substrate processingaccording to claim 14, wherein the etching gas is for etching siliconnitride film on the substrate, and the additional gas having theproperty of protecting the side faces of projections is nitrogen gas.18. The method of substrate processing according to claim 12, for makinglines in a thin film on the substrate by etching.
 19. The method ofsubstrate processing according to claim 12, wherein the pressure atwhich the substrate is processed in the processing vessel is regulatedto 1.3-40 Pa.
 20. A computer program for allowing a computer to performa method of substrate processing, the method of substrate processingbeing for processing a substrate by the use of a substrate processingsystem comprising, a processing vessel, a table that is placed in theprocessing vessel and on which a substrate will be placed, a gas supplyunit set on the top of the processing vessel facing the table, includinga center section that corresponds to the center portion of the substrateand has a large number of gas-jetting pores, and a peripheral sectionthat corresponds to the peripheral portion of the substrate and has alarge number of gas-jetting pores, a first-gas supply means of supplyinga common gas to the center and peripheral sections of the gas supplyunit at flow rates separately regulated, a second-gas supply means ofsupplying an additional gas, in addition to the common gas, to theperipheral section of the gas supply unit, and a means of evacuating theprocessing vessel, the method comprising the steps of: supplying to thesubstrate from the center and peripheral sections of the gas supply unitthe common process gas that has been supplied to the two sections by thefirst-gas supply means at flow rates separately regulated, supplying, inaddition to the common process gas, the additional gas that has beensupplied to the peripheral section of the gas supply unit by thesecond-gas supply means, to the substrate from the peripheral section,and evacuating the processing vessel with the means of evacuating theprocessing vessel, the distance from the center of the center section ofthe gas supply unit to the outermost gas-jetting pores in the centersection being 53% or more of the radius of the substrate.
 21. A storagemedium in which a computer program for allowing a computer to perform amethod of substrate processing is stored, the method of substrateprocessing being for processing a substrate by the use of a substrateprocessing system comprising: a processing vessel, a table that isplaced in the processing vessel and on which a substrate will be placed,a gas supply unit set on the top of the processing vessel facing thetable, including a center section that corresponds to the center portionof the substrate and has a large number of gas-jetting pores, and anperipheral section that corresponds to the peripheral portion of thesubstrate and has a large number of gas-jetting pores, a first-gassupply means of supplying a common gas to the center and peripheralsections of the gas supply unit at flow rates separately regulated, asecond-gas supply means of supplying an additional gas, in addition tothe common gas, to the peripheral section of the gas supply unit, and ameans of evacuating the processing vessel, the method comprising thesteps of: supplying to the substrate from the center and peripheralsections of the gas supply unit the common process gas that has beensupplied to the two sections by the first-gas supply means at flow ratesseparately regulated, supplying, in addition to the common process gas,the additional gas that has been supplied to the peripheral section ofthe gas supply unit by the second-gas supply means, to the substratefrom the peripheral section, and evacuating the processing vessel withthe means of evacuating the processing vessel, the distance from thecenter of the center section of the gas supply unit to the outermostgas-jetting pores in the center section being 53% or more of the radiusof the substrate.